Problem Description
Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge).
In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n.
Input
The input will consist of a series of integers n, one integer per line.
Output
For each case, output SUM(n) in one line, followed by a blank line. You may assume the result will be in the range of 32-bit signed integer.
Sample Input
1
100
Sample Output
1
5050
#include <stdio.h>
int main()
{
int n;
while(scanf("%d",&n)!=EOF)
{
int ans = 0;
if(n%2==0)
ans=n/2*(n-1)+n;
else
ans=(n-1)/2*n+n ;
printf("%d\n\n",ans);
}
}
